linux-kernel - Re: [PATCH v4 4/6] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 9 Sep 2014 15:13:07 +0800
From:	tangchen <tangchen@...fujitsu.com>
To:	Gleb Natapov <gleb@...nel.org>
CC:	<mtosatti@...hat.com>, <nadav.amit@...il.com>, <jan.kiszka@....de>,
	<kvm@...r.kernel.org>, <laijs@...fujitsu.com>,
	<isimatu.yasuaki@...fujitsu.com>, <guz.fnst@...fujitsu.com>,
	<linux-kernel@...r.kernel.org>, <tangchen@...fujitsu.com>
Subject: Re: [PATCH v4 4/6] kvm, mem-hotplug: Reload L1' apic access page
 on migration in vcpu_enter_guest().

Hi Gleb,

On 09/03/2014 11:04 PM, Gleb Natapov wrote:
> On Wed, Sep 03, 2014 at 09:42:30AM +0800, tangchen wrote:
>> Hi Gleb,
>>
>> On 09/03/2014 12:00 AM, Gleb Natapov wrote:
>>> ......
>>> +static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
>>> +{
>>> +	/*
>>> +	 * apic access page could be migrated. When the page is being migrated,
>>> +	 * GUP will wait till the migrate entry is replaced with the new pte
>>> +	 * entry pointing to the new page.
>>> +	 */
>>> +	vcpu->kvm->arch.apic_access_page = gfn_to_page(vcpu->kvm,
>>> +				APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
>>> +	kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm,
>>> +				page_to_phys(vcpu->kvm->arch.apic_access_page));
>>> I am a little bit worried that here all vcpus write to vcpu->kvm->arch.apic_access_page
>>> without any locking. It is probably benign since pointer write is atomic on x86. Paolo?
>>>
>>> Do we even need apic_access_page? Why not call
>>>   gfn_to_page(APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT)
>>>   put_page()
>>> on rare occasions we need to know its address?
>> Isn't it a necessary item defined in hardware spec ?
>>
> vcpu->kvm->arch.apic_access_page? No. This is internal kvm data structure.
>
>> I didn't read intel spec deeply, but according to the code, the page's
>> address is
>> written into vmcs. And it made me think that we cannnot remove it.
>>
> We cannot remove writing of apic page address into vmcs, but this is not done by
> assigning to vcpu->kvm->arch.apic_access_page, but by vmwrite in set_apic_access_page_addr().

OK, I'll try to remove kvm->arch.apic_access_page and send a patch for 
it soon.

BTW, if you don't have objection to the first two patches, would you 
please help to
commit them first ?

Thanks.

>
> --
> 			Gleb.
> .
>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/